The invention relates to methods of adhering solvent-dilutable polyurethane, silicone-polyurethane copolymer, or silicone-polycarbonate copolymer elastomers to a cured silicone body, and more specifically, to methods of making permeation-resistant laminates from polyurethane, silicone-polyurethane copolymer, or silicone-polycarbonate copolymer elastomers and silicone elastomers and to products produced by such methods.
In the medical field, there is a need for an improved biologically-acceptable, permeation-resistant material which could be used to make items such as the shell or envelope of fluid-filled prostheses or gas- or liquid-filled balloons or balloon portions of other devices. The resistance to permeation of silicone gel, air, or other fluids through the wall of a prosthesis or inflatable device is highly desirable to reduce gradual deflation or unnecessary exposure of tissues surrounding an implanted prosthesis to the permeating interior materials. In the specific case of an air-filled intra-gastric balloon, such as those used to treat morbid obesity, having resistance to the permeation of air through the balloon will decrease deflation and, thus, the need to periodically re-fill the balloon with air.
A breast prosthesis is disclosed in U.S. Pat. No. 4,172,298 which comprises a member formed of an additive cross-linking two-component silicone rubber of an adhesive gelatinous consistency covered on each side by a plastic film, the plastic films being welded to each other along the rim of the member. The patent discloses that polyurethane is particularly useful as the plastic film. U.S. Pat. No. 4,247,351 discloses a process for manufacturing artificial breasts which have cups sheathed by plastic sheets (such as polyurethane) and into which the silicone rubber composition is charged. During the vulcanization of the rubber, the edges of the sheets are forced together and joined by welding. Similarly, U.S. Pat. No. 4,258,442 discloses that a breast prosthesis consisting of silicone rubber may be surrounded by an elastic plastic sheet, especially a foil of polyurethane. Similar to these patents is U.S. Pat. No. 4,701,230 which describes a prosthesis comprising an outer or front sheet, an intermediate sheet, and an inner or rear sheet. The sheets are sealed together at their peripheries. The patent states that the intermediate sheet may be made of polyurethane film. Silicone gel compound is injected into the compartment formed by the outer sheet and the intermediate sheet and is cured.
Similarly, U.S. Pat. No. 4,249,975 discloses a process for manufacturing artificial breasts which uses a two-component silicone rubber composition capable of a crosslinking addition reaction, in which the artificial breast has cups sheathed by plastic sheeting layers (formed of, e.g., polyurethane) initially joined by welding except for one opening through which the silicone composition is introduced under pressure. The silicone composition is then vulcanized and the opening closed by welding.
Some permeation-resistant silicone-gel-filled prostheses are known in the art. Specifically, U.S. Pat. No. 4,455,691 discloses a prosthesis comprising a flexible sac and a silicone gel contained within the sac. The wall of the sac is comprised of a layer of silicone elastomer which substantially impedes the migration of the silicone gel from the sac. Silicone elastomers disclosed as suitable materials for impeding the migration of silicone gel from the sac are composed of reaction products of dimethylpolysiloxane and either 3,3,3,-trifluoropropylpolysiloxane, diphenylpolysiloxane, or methylphenylpolysiloxane. The patent describes that the prosthesis may be made by first making a sac by dipping a mandrel into a solvent dispersion of unvulcanized silicone elastomer, allowing the solvent to evaporate from the coated silicone elastomer, then dipping the coated mandrel into a dispersed elastomer which constitutes a second continuous layer (either layer is formed of the permeation-resistant material). All coats are preferably cured together after the coating has been built up as desired. Alternatively, the prosthesis is said to be made by dipping a mandrel into a dispersion of unvulcanized silicone elastomer, then curing the coated elastomer material to form a sac, then injecting a dispersion of the permeation-resistant material into the cured sac and evenly swirling the dispersion (slush-coating) over the inside of the inflated sac, and then curing the slush-coated sac.
Similarly, Canadian Pat. No. 1,199,451 discloses a silicone-gel-filled silicone rubber container possessing a reduced tendency to exhibit surface-bleed which includes an essentially continuous barrier layer of a composition consisting essentially of a fluorine-containing organopolysiloxane situated between the interior of the container and the gel filling the container.
Although these patents describe permeation-resistant prostheses, there continues to be a desire for an improved product, a prosthesis with a higher permeation resistance potential and greater strength.
U.S. Pat. No. 4,592,755 discloses a prosthesis comprising a leak-proof flexible sac containing a polysiloxane gel and/or oil, said sac comprising a continuous cured polyfluoroalkoxy substituted phosphazene elastomer wall which is substantially impermeable to said gel or oil. In one embodiment described, the prosthesis wall is a two-layer wall, the inner layer comprising a cured polyfluoroalkoxy substituted phosphazene elastomer barrier layer and the outer layer comprising a cured polysiloxane elastomer.
A method of adhering a curable urethane to a room-temperature curable silicone rubber is disclosed in U.S. Pat. No. 4,163,072. The patent describes that, while the silicone rubber is in an uncured state and any solvent present has been allowed to evaporate without curing the silicone rubber, a solvent-resistant cover coating which cures by heat or reaction with moisture, such as polyurethane or epoxy is applied, and then the resulting structure is treated so that the two layers cure simultaneously. The types of silicone rubbers taught as suitable for the technique are limited to room-temperature, moisture-curable silicone rubbers.
U.S. Pat. No. 4,312,920 discloses a blood contacting layer formed by dipping a wax form into a filler-free silicone rubber, curing the silicone rubber, then dipping the coated form into a segmented polyurethane, heat curing the coated form, removing the wax form, then removing the silicone rubber lining, leaving a binary alloy blood contacting surfaced polyurethane sac. The patent states that it appears that the polyurethane solvent has a modifying effect on the filler-free silicone rubber and permits the migration of the polyurethane and silicone rubber species. N-N dimethyl acetamide, formamide, and tetrahydrofuran are mentioned as possible suitable polyurethane solvents.